Everything You Need to Know About Battery Balancing
What is Balancing?
Balancing is equalizing the voltage of individual cells in a battery system. It means bringing each cell's voltage closer to the pack's average voltage.
Why is Balancing Necessary?
In battery systems, cells are often connected in series to achieve higher voltage levels that meet the load requirements. For example, a battery pack consists of 16 individual cells in series. Cell internal resistance will differ due to the manufacturing date, environment, electrode thickness, and electrolyte volume.
According to Ohm’s Law, differences in internal resistance lead to differences in cell voltages. In a series circuit, the current is constant throughout the circuit during charging and discharging. Cells with higher internal resistance will reach their voltage limit value sooner during charging and drop to their voltage limit value faster during discharging. This phenomenon represents the inconsistency within a battery system.
Such inconsistencies can cause irreversible damage to the battery pack or even catastrophic failure. Therefore, balancing is essential to ensure cell voltages approach or within safe upper limits, thus safeguarding the battery system's operation.
Benefits of Balancing
One of the primary purposes of balancing is to enhance the safety of the battery system. Additionally, balancing can improve the system's usable capacity.
One of the primary purposes of balancing is to enhance the safety of the battery system. Additionally, balancing can improve the system's usable capacity.
How does balancing increase usable capacity?
Without balancing, when one cell in a pack reaches its upper voltage limit during charging, the monitoring circuit signals the control system to stop charging, leaving the pack undercharged.
Without balancing, when one cell in a pack reaches its upper voltage limit during charging, the monitoring circuit signals the control system to stop charging, leaving the pack undercharged.
With balancing, the Battery Management System (BMS) continuously monitors voltage differences and upper voltage limits. Once the preset voltage difference is reached, the balancing function activates. The balancer regulates the charging current for individual cells, reducing charging for cells with higher voltages and increasing it for those with lower voltages. This mechanism extends the charging time and increases the system's chargeable capacity, thus improving its usable capacity.
From a State of Charge (SOC) perspective, without balancing, the SOC range is typically limited to 20% to 80% for safety reasons, providing only 60% usable capacity. With balancing, the SOC range can be expanded from 5% to 95%, increasing usable capacity to 90%. This means the battery pack's usable capacity is significantly enhanced.
Therefore, balancing improves the Depth of Discharge (DOD), making the battery system more efficient.
It's important to note that balancing only equalizes cell voltages to the average value of the pack and does not alter the inherent characteristics of the cells. Can balancing slow down cell degradation? There is no conclusive data in the industry to confirm this, and further research is needed.
Additionally, many BMS manufacturers are pushing to increase balancing currents, to improve balancing efficiency. However, even large balancing currents cannot save low-quality cells. Overstating the role of balancing is incorrect and irresponsible to consumers.
The True Role of Balancing
Battery system balancing primarily ensures the safety of the energy storage system and then increases usable capacity. It is a maintenance and compensatory measure, with minor adjustments during each charge and discharge cycle to mitigate cell differences. Continually balancing will lead to unnecessary battery consumption and shortened lifespan.
Battery system balancing primarily ensures the safety of the energy storage system and then increases usable capacity. It is a maintenance and compensatory measure, with minor adjustments during each charge and discharge cycle to mitigate cell differences. Continually balancing will lead to unnecessary battery consumption and shortened lifespan.
Release time: 2025-04-03
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